The invention generally relates to light sources for generating two high-intensity trains of laser pulses at different wavelengths, wherein the two pulse trains are temporally synchronized and have a stable phase relation.
Such light sources are applied, for example, in coherent anti-Stokes Raman scattering (CARS) microscopy. CARS is a nonlinear imaging technique that offers chemical selectivity and three-dimensional resolution. In order to obtain a CARS signal, two light waves with different frequencies are spatially and temporally overlapped in a sample. Then, a vibrational level at the frequency corresponding to the difference of the frequencies of the two light waves is excited. This results in a molecule-specific response and thus provides chemically selective contrast. Tightly focusing the two light waves in a scanning microscope, the CARS signal is generated exclusively in the focus volume, which enables high three-dimensional spatial resolution.
P. Groβ et al (Appl. Phys. B, 2010, vol. 101, pp. 167-172) describe a laser light source, which is based on a single Titanium-Sapphire femtosecond laser oscillator. A second wavelength is derived from the primary laser by soliton self-frequency shift in a micro-structured optical fiber (MSF) and subsequent amplification. The second wavelength is de-tuned by varying the output power of the Titanium-Sapphire laser as the soliton dynamics within the MSF depend on the power of the radiation propagating in the MSF.